2. Field of the Invention
This invention relates to digitally controlled inverter circuits and, more particularly, to the logical control of voltage generation at remote locations where centralized power supplies are not readily available.
2. Description of the Prior Art
In many telephone applications it is necessary to provide certain direct current control voltages to operate equipment located at a station set. Coin stations, for example, require both positive and negative sources of 100 volts to operate coin collect and coin return relays at the coin station.
If it is desired to service such coin stations through subscriber loop multiplex systems such as that disclosed in the copending application of J. E. Dail Ser. No. 645,022 filed Dec. 29, 1975 and assigned to applicant's assignee, these voltages cannot be supplied directly from the central office. It is therefore desirable to generate direct current control voltages at the remote locations which are under the control of supervisory information from the central office. Such voltage supplies must be small, compact, and inexpensive, as well as efficient and reliable.
In order to regulate the output of a power supply of this type, it has been common in the art to provide regulation by controlling the width or duty cycle of the driving signal. This regulating arrangement has the disadvantage that the portion of conversion inefficiency resulting from switching losses is not directly proportional to output power. The fractional loss of power due to switching losses increases with decreasing output power. A further disadvantage is the often necessary requirement that the duty cycle of the two bipolar driving signals be carefully matched or controlled to avoid applying a direct current offset voltage to the inverter transformer with the possibility of saturating the transformer's magnetic core.